CompilationUnit

CompilationUnit is a term used in programming language tooling to denote the root node of the syntax tree for a single source file, commonly referred to as a compilation unit. In Java tooling, the CompilationUnit is the top element of the Java abstract syntax tree (AST) produced by parsers such as Eclipse JDT. It serves as the container for the contents of one source file and provides a structured view of its structure.

In a typical Java CompilationUnit, the content includes an optional package declaration, zero or more import declarations, and one or more type declarations such as classes, interfaces, enums, or annotation types. The unit may also carry information about comments and the source code's positional metadata, enabling mapping between AST nodes and the original source text. The exact fields and organization can vary between implementations, but the unit is always the entry point for traversing the file’s syntactic elements.

The CompilationUnit is used in tasks such as compilation, static analysis, refactoring, and code navigation. By visiting the types, imports, and package information contained in the unit, tools can analyze dependencies, resolve bindings, generate documentation, or transform code. It also often includes mechanisms to associate comments with relevant code positions, which can be important for documentation generation and code formatting tools.

Parsing a source file typically yields one CompilationUnit, which can then be traversed by AST visitors or query via APIs provided by the tooling framework. While the general concept applies across languages and tooling, the exact structure and available metadata of a CompilationUnit depend on the specific parser or IDE framework in use.